U.S. Pat. No. 4,210,156 to Elmer T. Bennett shows a blood sampler for collecting up to two milliliters of blood. This sampler functions by piercing the skin superficially and using a vacuum effect to collect the resulting small pool of blood formed on the skin surface. The vacuum for this sampler is created by the operator sucking on a mouthpiece. The sampler includes a collection vessel for containing the blood sample. The vessel includes a substantially transparent tapered end portion and a top portion. The two portions are assembled to form a single cavity. The tapered end portion has an opening through which blood enters from the skin surface. The top portion has a channel which communicates with the suction tube.
A variation on the Bennett '156 sampler is shown in FIG. 1 herein. This sampler is includes a small projection 11 that extends outward from the rim of the inlet tip of the tapered portion of the collection vessel. This outward projection is effective for collecting the small pool of blood from the skin surface.
Becton, Dickinson & Co. of Shipshewana, Ind., markets a device under the trademark "Vacutainer". This device generally comprises three parts: an intravenous needle portion, a vacuum tube, and a holder. The intravenous needle portion includes a length of hollow metal tubing, one end of which forms a skin-piercing intravenous needle and the other end of which is ensheathed in a flexible sleeve. This ensheathed end is designed to pierce a rubber stopper in the vacuum tube which forms a collection vessel. The vacuum tube is an evacuated glass testtube. The holder holds the vacuum tube in place relative to the intravenous needle so that the vacuum tube may be pressed down on the ensheathed end thereof. In operation, the skin piercing end of the intravenous portion is inserted into a vein. Once the tip of the intravenous needle has pierced the vein, the vacuum tube is firmly pushed forward in the holder so that the ensheathed end of the needle is forced through the rubber top of the vacuum tube as the sleeve surrounding the needle is compressed. The vacuum tube must be pushed down firmly in order to pierce the rubber top. This operation requires a substantial degree of manual dexterity on the part of the phlebotomist. Blood is drawn through the needle and into the vacuum tube by a suction force created by the vacuum inside the tube.
The "Vacutainer" device is designed to sample relatively large quantities of blood, compared to the '156 sampler. Like the '156 sampler, the "Vacutainer" device uses a vacuum principle to extract blood, but because it extracts blood by artificial suction through the needle, it has numerous disadvantages.
It is known that blood cells may be damaged in the course of vacuum-drawing, thus affecting the integrity of later analysis. For example, hemolysis of red blood cells may occur as the cells are forced under pressure through the narrow orifice of the drawing needle. Thus, vacuum blood-drawing is generally conducted through larger gauge needles, in order to minimize hemolysis. Larger gauge needles are relatively more uncomfortable to the patient.
In addition to hemolysis of red blood cells, vacuum drawing may result in other abnormalities which tend to confound interpretation of data relying on visual examination of cells, e.g. as in the differential leukocyte count. The appearance of cell abnormalities or cell fragments, which may be regarded as an indication of illness, may actually comprise artifact caused in the vacuum drawing process. For instance, red blood cell abnormalities such as clumping or stacking, which may otherwise be indicative of disease, may in actuality be caused by the drawing process, and not any disease.
Another disadvantage of vacuum tube samples may occur when the vacuum is lost for any reason during the blood-drawing process. If this occurs, the needle must be withdrawn from the patient, and the procedure must be repeated.
The use of vacuum tubes may also increase health hazards to both laboratory technicians and the general public. For example, small amounts of blood emit from the needle hole in the vacuum tube's rubber top as the collection tube is withdrawn from operative engagement with the sheathed needle. Contact with even these minute amounts of blood may be hazardous to health care personnel. Particularly, contact may be incurred with highly infectious specimens, such as specimens withdrawn from hepatitis patients, AIDS patients and the like. Moreover, it has been observed that when the rubber top of a vacuum tube is removed in the laboratory for sampling, the rapid equalization of pressure between the still partially evacuated tube and the atmosphere may cause blood aerosols to be emitted. Contact by laboratory personnel with these vapors may be hazardous.
Vacuum blood-drawing may also result in a distorted analysis of blood components. Samples drawn under vacuum may indicate a disproportionately high level of the lighter blood components such as platelets, immature cells and blood gases. These lighter blood components, particularly blood gases, are withdrawn at a higher rate than the heavier components. The levels of the lighter blood components may thus be artificially enriched in the sample. As a result, blood samples for gas analysis are typically drawn in specialized syringes, and only from arterial blood sources.
Additionally, since blood rushes into evacuated tubes at a relatively rapid rate, the amount of blood drawn by means of vacuum tubes may not be controlled with precision.
The preferential enrichment of lighter blood components in vacuum tube samples is particularly troublesome when like volume samples must be drawn from the same patient at various time intervals. The inability to accurately draw precisely the same volume of blood each time using vacuum tubes, coupled with the selective enrichment of the lighter blood components inherent in vacuum-drawing, may confound interpretation of such serially-drawn samples.
Vacuum tubes are typically fabricated from glass, and are generally sized for drawing 5, 10 and 15 ml specimens. The use of glass containers for blood-sampling has several disadvantages. First, they must be centrifuged only at relatively slow speeds, about 3,500 r.p.m. Second, vacuum tubes are not easily marked for identification purposes. This make illegally disposed medical waste contained in vacuum tubes difficult to trace. Third, vacuum tubes have limited shelf life, since the vacuum is inevitably lost through prolonged storage. Fourth, for analyses requiring uncoagulated blood, vacuum, tubes contain anticoagulant which is deposited in the tube bottom as a liquid, solid or powder. Because of the manner in which vacuum tubes are filled, the anticoagulant may not mix evenly with the blood, resulting in coagulation of some portions of the sample.
Newer blood analysis equipment requires smaller specimens (generally 5 to 20 microliters) than the relatively large blood volumes typically drawn with vacuum tubes. This excess blood, which is not used, increases the cost of medical waste processing. Typically, blood collected in vacuum tubes must be thereafter transferred to smaller containers designed for use in the various laboratory analyzers. Such additional manipulative steps and handling of blood samples is undesirable from the standpoints of laboratory efficiency and safety.
Finally, in elderly persons and neonates, it may be impossible to utilize vacuum tube type collection. The relatively strong vacuum may lead to collapse of the vein being sampled. Moreover, it is known that the sudden surge of blood flow into evacuated collection tubes is stressful to the cardiac system of neonates and infants, and may result in cardiac arrest.